Stationary vehicles such as cargo trucks, trailers, and airplanes are required to be restrained from movement during loading and unloading by means of chocks placed under the wheels. Chocking of the wheels prevents movement of the vehicle during loading and unloading, brake failure, or inclined parking. The wheel engagement surface of a chock is typically a flat incline or concave shape to generally match the radius of the wheel.
One noted problem with such chocks is that, even though the wheel may be properly chocked, dynamic forces during loading or unloading, for example, may push the chock horizontally along the ground. This action can be extremely dangerous, since the vehicle is momentarily not secured from movement, potentially causing a serious accident, bodily injury, or even death.
Another common problem with wheel chocks, particularly during loading operations with trucks, trailers, or aircraft, is that the additional vehicle gross weight may cause the chock to become wedged in place and not removable by hand.